And from damascus, we head now to iran. And, a new, defiant challenge from that country, a country filled with nuclear ambition. And once again, abc's david muir is reporting live from tehran tonight. David? Reporter: Diane, good evening again from iran this evening. The inspectors who say they've discovered advanced centrifuges installed at one of iran's main nuclear facilities. They say it's proof that iran can speed up the process to a nuclear weapon. Iran says it has no such ambition, but the state department, diane, reacting quickly tonight, calling this further escalation, a provocative step, just days before the u.S. And iran are back at the negotiating table. And tonight, right here, you'll hear from the iranian people with spoke with today, many of whom say they're the ones caught in the middle. Allowed rare access to the streets here, today, we went in search of one of the biggest pharmacies in central tehran, having heard life-saving medicine is now running out. Hello. Reporter: This doctor runs the pharmacy. Right now, we are running low on every category of medicine. Reporter: And he points straight to those tightening u.S. Sanctions, meant to force iran's leaders to change course on their nuclear program, now affecting everyone. Even patients buying medicine. All of it because money in and out of iran is nearly frozen. But because of that money flow, it has stopped some of the drugs from coming in? Yes, because you are a manufacturer of a drug, you want your money. When I can't pay you, how can you send the medicine to me? Reporter: And that's all because of the sanctions? That's right. Reporter: Cameras are rarely allowed free reign in iran. But we ask him to allow us inside the pharmacy and he takes us. Is this crowd typical, the size of this crowd? Immediately, we see the lines as we snake our way behind the counter to the back. Where not only are they low on many medications, they have run out of several cancer drugs. Colon cancer, you don't have? We don't have. Reporter: And what do you give instead? We don't have much. Reporter: And by mid-day alone -- how many people have been asking for it? 40 people. Reporter:40 people today have asked? And on the other side of the counter, the urgency in their faces. This man shows us the prescription for a loved one with leukemia. He took a cab from two hours away. When we did the math, with skyrocketing inflation here, that ride cost him more than $500. And you have gone to how many pharmacies? Translator: Over 20. Reporter: Over 20? And when we were there, he finally makes husband way to the window, where he is told there is none left. To come back saturday. You will go home with no medicine? "What can I do?" He asks. And as the sun set in tehran tonight, the sanctions meant to force the supreme leader, whose revered image hoffers over the city, into backing down on any nuclear images, are now forcing the people here to pay the price, too. We should point out that the government did not take us to that pharmacy today, in fact, we had to push to get our cameras inside. Police were waiting for us afterward, cheque for our paperwork to make sure not only we had been invited into iran, but more importantly, our camera, diane. And one other thing that struck me is that many of the customers, the patients there, offcamera, when we asked them who is to blame, often, they would say, we don't know who is to blame, but we should point out that we are the ones that feel we are trapped in the middle of this standoff, diane.

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